This invention relates to coal mining, and more particularly to an improved horizon control sensor for detecting engagement of the cutting tool of a coal mining machine with rock or other material enclosing a coal seam.
Underground coal mining is done with longwall drum shearers and continuous miners which are controlled by an operator to maintain the cutting tools in the undulating coal seam. The most critical need for increasing the productivity and safety of the underground mining of coal is an improved sensor to control the elevation of the drums on the shear loader machine of a longwall mining machine and the elevation of a continuous mining machine. Such a device would allow mining to be done at the maximum operating speed of the machine and not be slowed down by the operators, would reduce the waste material taken from the floor and ceiling while maximizing the amount of coal taken, and is the key to automated coal mining machines which will allow the operator to run the machine while located outside the hazardous face area.
Two systems for the automatic detection of the interface between coal and surrounding rock are the sensitized pick and the nucleonic sensor. The sensitized pick is a strain gage transducer and earlier attempts to develop a working device proved feasibility but it was not further developed. The nucleonic sensor relies on a gamma ray back scattering technique that measures the remaining coal thickness by reflecting gamma rays off the coal-rock interface. This system was developed into a marketable product but does not properly do the job. U.S. Pat. No. 2,944,804 to Persson discusses monitoring the vibration of the rotating cutting tool of a mining machine by accelerometers mounted on the machine to sense the higher amplitude of vibration exceeding a preset level when the cutting bit enters rock. Tool vibration amplitude differences between coal and rock are dependent on material hardness which is not a unique discriminant. Many coal fields are enclosed in material softer than rock and cannot be followed by measuring higher vibration amplitude alone. This combined with amplitude vibrations which occur due to machine movements, dull tools, and other external operations make this concept risky.